The present invention relates to methods of applying water resistant coatings to a heat exchanger coil in general, and in particular to methods of applying porcelain ceramic coatings to mild steel heat exchanger tubes, and the equipment for effecting such coatings.
Hot water is used domestically for bathing, cleaning and heating, and commercially for similar purposes. In domestic and commercial water heating, water is normally heated in a water tank with a central flue extending upwardly from a combustion chamber located beneath the water tank. The water in the tank is heated through thermal conduction from the tank bottom and the central flue. There are, however, many circumstances in which it is desirable to heat water indirectly in a storage tank. For example heat from a boiler which heats recirculating water for domestic or commercial space heating, can be used to heat water in a so called indirect-fired water heater. In an indirect-fired water heater or storage tank, a heat exchanging coil is positioned within the water tank and hot water from the boiler or other source is circulated through the heat exchanging coil. Another source of heat for domestic hot water is that of a solar thermal system which stores heat gathered from the sun. These systems also require water storage tanks which can be heated indirectly by means of a heat exchange coil. Geothermal systems also require storage of heat recovered from geothermal reservoirs, and thus make use of water storage tanks with heat exchanging coils.
Domestic hot water appliances are typically manufactured from mild steel and are protected from potable water—which may contain dissolved oxygen—by a glass or enamel coating. The coating is applied as a slip i.e., a water and ceramic slurry, which is dried and then fired to form a glass coating which protects the metal of the tank from corrosion and oxidation. Secondary protection is often provided by sacrificial anodes of, for example, magnesium.
A coating is typically applied to heat exchanger coils by spraying the coil. This method, however, involves considerable labor, results in over spraying of the coating, and lacks uniformity in the applied coating. What is needed is an automated system to uniformly coat water storage heat exchanging coils which minimizes cost and waste.